An optically coupled isolation device, which includes an optical transmitting unit with an analog-digital conversion circuit and an optical receiving unit, may transmit a signal in a state where an input terminal and an output terminal are insulated from each other.
A drastic current variation in an analog-digital conversion circuit and the like generates a noise voltage through electromagnetic induction. The noise voltage is input into a circuit through, for example, capacitive coupling caused by parasitic capacitance between leads or magnetic coupling between leads.
In some circumstances, the isolation device may fail when the noise voltage increases.